1. Field of the Invention
The invention relates to a magnetic resonance apparatus having a quadrature mode radio-frequency coil system in which two coils are incorporated in an electric switching circuit for generating and/or detecting magnetic resonance signals.
2. Description of the Prior Art
Of interest is copending application Ser. No. 333,057, filed Apr. 3, 1989 entitled Quadrature RF Coil system for MR Apparatus in the name of Van Vaals and assigned to the assignee of the present invention. Such an apparatus is disclosed in EP 196134 corresponding to U.S. Pat. No. 4,7l2,O69, by the same inventor as herein. The advantages of the quadrature coil system described in said Specification in a magnetic resonance apparatus are a better signal-to-noise ratio and a reduction of eddy current disturbances and of the required supply energy. The very disturbing phase shift between excitation and detection occurring when quadrature coils are used in magnetic resonance measurements is avoided there by incorporating in a switching circuit for matching impedance and phase upon excitation and detection a first 1/4 .mu. conductor connecting the first and the second coil and a second 1/4 .mu. conductor connecting the second coil. A drawback of this solution is that the 1/4 .mu. conductors constitute comparatively clumsy elements and for each frequency must have a different length.